Fix macOS Python 2.7 build (#2140)
Fix macOS Python 2.7 build (#2140)

Currently Python 2.7 tests & builds were run twice for Linux instead.

Swap configuration to macOS 10.15, in par with Python 3 workflow,
and to make Process.environ tests pass (broken in macOS 11+).

Signed-off-by: Ben Raz <8e2d24b5c2de1cc69ee336d6ddf448e6013fc118@gmail.com>

giampaolo/psutil,giampaolo/psutil